1) Field of the Invention
The present invention relates generally to guard members for shielding the propeller of an outboard motor. More specifically, the present invention relates to a propeller guard which is designed for maximizing the performance characteristics of an outboard motor.
2) Prior Art
The propeller of an outboard motor typically rests below the bottom surface of the boat when in use, and propels the boat through the water. Due to its position during operation, the propeller tends to be very suspectable to damage from under water objects such as rocks, sandbars, marine life and the like. If the propeller becomes damaged due to its impingement on underwater objects, it may become unable to perform as designed. The need for repair and/or replacement of a propeller damaged thus generally occurs at very inconvenient times and is always very expensive. Therefore, a need exist to develop a guard which can protect the propeller of an outboard motor and prevent its being damaged by underwater objects.
Also, the propeller of an outboard motor spins at an extremely high RPM during use. Should a passenger, skier, swimmer or other person be accidentally hit by the propeller during operation of the motor, serious injury will inevitably result. Therefore, a guard which will inhibit accidental contact of a person with the propeller to prevent accidental bodily injury is also needed.
Many prior art attempts have been made to solve the above problems. Several prior art devices which are representative of the many previous attempts to develop a prop guard responding to the above-identified needs are shown in U.S. Pat. No. 2,551,371 to Grieg; U.S. Pat. No. 2,963,000 to Fester; U.S. Pat. No. 2,983,246 to Manley; and, U.S. Pat. No. 4,078,516 to Balius. In each of these devices, an enclosure, generally including a hollow cylindrical member, is attached to the outboard motor so as to surround the propeller. The devices are designed to allow water to have fluid flow access to the propeller in order to allow the propeller to function as designed. Although these devices are somewhat successful in preventing damage to the propeller by preventing contact of the propeller with underwater objects, several severe drawbacks nevertheless remain. Most importantly, each of these devices tend to severely reduce the performance characteristics of the outboard motor.
As is well understood, an outboard motor pushes a boat forward in reaction to the propellers of the motor forcing water backwards. However, an outboard motor which also includes a propeller guard is inhibited in its performance due to the fact that water flowing past the propeller tends to be blocked or directed away from the propeller by the guard. Also, water impinging on the guard during operation of the motor increases the drag characteristic thereof, thus decreasing performance. Further, the presence of the guard, since not necessarily designed as an integral part of the motor, can cause instability, vibrations, control degradation, and unpredictability of motor response during use. Finally, prior art propeller guards are attached to the motor in such a manner as to be incapable of preventing damage or failure of the attachment members during high speed use. Accordingly, it is needful that a propeller guard be developed and designed which affords protection against contact between the propeller and underwater objects, and which at the same time is designed so as to maintain or improve motor performance characteristics such as steering, top end speed, planing, acceleration, and durability.
U.S. Pat. No. 4,680,017 to Eller, attempts to address the problem of maintaining and/or improving performance characteristics of the motor through the design of a propeller guard. The propeller guard of the Eller invention functions to prevent radial dissipation of water passing through the propeller, to thereby cause all water to be directed in a linearly rearward direction as it passes through the propeller. The intent is to ensure that all the water passing through the guard is useful in generating forward motion of the boat. However, in operation, the drag characteristics of Eller's propeller guard tend to off-set any advantages of its use. Further, control characteristics of Eller's motor are significantly degraded due to the presence and design of Eller's propeller guard.
U.S. Pat. No. 5,098,321 to Taylor, Jr., a co-inventor of the present application, also attempts to address the problem of maintaining and/or improving performance characteristics of the motor through the design of a propeller guard. The Taylor, Jr. invention includes many improvement over prior propeller guards in this respect including the use of a series of evenly spaced openings around the ring portion of the guard which are formed to allow water to pass therethrough during operation so as to increase the water volume passing the propeller and to avoid cavitation during turning. The present invention builds upon the design features in the Taylor, Jr. invention to further improve fluid flow past the propeller. Increase water pressure at the propeller plate surfaces, prevent cavitation due to the presence of the propeller guard, and improve steering, top end speed, planing, acceleration, and durability of the motor.